The present invention relates generally to modelling and displaying techniques in the graphic processing and more particularly to a displaying method and apparatus suited profitably for three-dimensional computer graphics.
In the field of three-dimensional computer graphics, speeding-up of the processing involved in displaying graphic models of bodies is attempted by taking advantage of the fact that the individual models existing in space occupy only localized regions which are unlikely to overlap one another, as is discussed in "Periodical of the Information Processing Society of Japan", Vol. 25, No 6 (1984), p. 948. More specifically, there is reported a graphic processing method according to which a delimited space such as, for example, a circumscribing rectangular parallelepiped is defined for a model of a body to be displayed, wherein the processing for searching the model is limited only to the inner space of the circumscribing rectangular parallelepiped. This method is certainly advantageous in that wasteful searching of a region located remotely from the model of concern can be avoided, whereby the processing for generating a graphic representation of the body can be speeded up.
Another method of speeding up the representation processing based on a similar concept is disclosed in Japanese Patent Application Laid-Open No. 79477/1985 (JP-A-60-79477). According to this known method, searching of a model of a body on a screen is limited to a rectangular region enclosing the model with the aim to enhance the speed of the processing for displaying the same. Further, JP-A-61-139890 discloses a high-speed display processing procedure in which the range to be searched for a model of body to be displayed is also limited in view of the localized disposition thereof while uniformity of the searching process is taken advantage of for speeding up the processing.
On the other hand, in a system disclosed in "Computer Graphics", Vol. 16, No. 3 (1982), pp. 9-18, a plurality of models are allocated to one and the same body to be displayed. More specifically, an operator can prepare a plurality of models having different degrees of detail to be allocated to a same body and input the models in the system which in turn determines discriminatively for the display the model having a desired degree of detail depending on the size of the body on a screen.
Of the prior art techniques described above, the high-speed display procedure based on the utilization of the localized disposition of the model suffers disadvantage in that the search is performed exactly even for a region which is defined for a model located sufficiently far from the visual point and which occupies only an extremely small area of a screen, resulting in the consumption of the time involved in such searching not being reducible by any appreciable degree as compared with the time taken for the searching of a region within which a model located sufficiently near to the visual point is defined. On the other hand, in the system capable of displaying a plurality of models having different degrees of detail, the processing itself can certainly be speeded up for the model located sufficiently remotely from the visual point. However, this system requires preparation and allocation of the models by the operator, increasing the number of interventions to be taken by the operator.